The present application claims priority to and incorporates by reference, in its entirety, PCT application no. PCT/GB00/02281, filed Jun. 12, 2000, which claims priority to Great Britain application no. 9913518.8, filed Jun. 11, 1999.
This invention relates to the controlling of undesired fore and aft oscillations of a motor vehicle.
When a motor vehicle is being driven, particularly with a manual transmission, there is a risk of undesired oscillations being produced in the drive train and transmitted to the vehicle, adversely affecting the comfort for the vehicle occupants. These oscillations affect comfort of the occupants within the vehicle, a factor often termed xe2x80x98driveabilityxe2x80x99.
To deliver good driveability it is necessary to reduce driveline disturbances (which produce hesitations and oscillations in the vehicle fore-aft dynamic response) allowing the vehicle to pull away, accelerate, decelerate and drive smoothly; this makes the vehicle feel more stable and refined.
The occurrence of these undesired fore and aft oscillations in a motor vehicle is sometimes termed xe2x80x98vehicle shufflexe2x80x99. It is an object of this invention to control and reduce vehicle shuffle.
Proposals have been made to reduce vehicle shuffle, but none of these have completely solved the problem. Furthermore a less than satisfactory solution can result in exacerbating or bringing to the driver""s notice the problem which might otherwise have remained unnoticed.
EP 0 802 317 describes a driveline damping system in which an engine speed is filtered to produce a derivative value. The derivative value is filtered again to remove values below a specified threshold, and the remaining signal is then subjected to amplification and then phase change to produce a signal which is fed to an engine ignition controller to reduce engine torque with the aim of dampening driveline oscillations.
Because the phase change takes place after the deadband filtering step and after the amplification step, the signal that is xe2x80x98phase compensatedxe2x80x99 will no longer be representative of the fluctuations which cause the oscillations.
From a control system perspective, the problem can be formulated as a disturbance rejectionxe2x80x94the disturbance being undesirable oscillations in motor/engine speed, torque and drive line speed and torque.
For a powertrain equipped with a mechanical throttle the engine torque response is open loop and is dominated by airflow response to throttle motion. The resulting change in engine torque will excite any oscillatory modes in the driveline, and external torque disturbances will have the same effect.
It is possible to shape the engine torque response in an open loop manner based on recognising and responding appropriately to the different classes of driver input demand. This can be thought of as working by reducing the energy spectrum of the engine torque into the driveline in that frequency range that includes the driveline modes. It has been found to be very effective on the heavier, faster manoeuvres.
According to the invention, there is provided a method of controlling undesired fore and aft oscillations of a motor vehicle by applying a torque control signal to a controller, the method comprising the steps of:
continuously sensing the speed of the vehicle motor and producing a signal representing the speed
analysing the speed signal
determining a mean value for the speed signal
identifying fluctuations from the mean value
filtering the signal to remove the mean value and to retain the fluctuations
applying a phase change to the filtered signal such as to align the torque control signal with the identified fluctuations
applying a deadband such that signals below a predetermined magnitude are ignored
amplifying the filtered and phase changed signal resulting from the deadband application to provide said torque control signal,
supplying torque control signal to the controller which controls the torque output of the vehicle motor.
All of these method steps can be implemented by software within an engine management system.
The software implementation of the method steps can be carried out in an engine management module of the vehicle.
The vehicle engine is preferably an internal combustion engine, in which case the torque output can be controlled by one or more of:
altering the spark timing
altering the air flow
altering the fuel flow.
The speed of the engine can be sensed from the change of crankshaft angle (delta crank angle interrupts).
The predetermined magnitude below which the deadband is established may be 5-10 rpm fluctuation from the mean rpm value.
A bias term may be applied to the control signal. Such a term reduces the power output of the engine by a predetermined amount, so that both advance and retard signals to the torque controller can be implemented.
The filtering step is carried out in two filtering stages; namely a first filtering stage which has the effect of removing xe2x80x98constant accelerationxe2x80x99 components of the signal, and a second filtering stage which has the effect of removing constant components of the signal.
The phase change can have a value between 50 and 70xc2x0, preferably 60xc2x0 and enables good gain and phase margin properties to be achieved for the control loop.
The invention also extends to an engine management system for managing the operation of a combustion engine in a motor vehicle, which system is adapted to receive an engine speed signal and to output a torque control signal to an engine torque controller, the system comprising:
means for analysing the speed signal
means for determining a mean value of the speed signal and for identifying fluctuations from the mean value
filtering means for filtering the signal to remove the mean value and to retain the fluctuations
means for applying a deadband such that signals below a predetermined magnitude are ignored
means for applying a phase change to the filtered signal such as to align the torque control signal with the identified fluctuations
amplification means for amplifying the filtered, and phase changed signal to provide said torque control signal, and
means for supplying torque control signal to the engine torque controller to control the torque output of the vehicle engine.
The engine speed signal is preferably derived from an engine crank angle sensor.
Still further, the invention extends to a motor vehicle having an engine, an engine speed sensor, an engine torque controller and an engine management system as set forth above.